Projectors are being used in various environments such as meeting rooms, class rooms, households, and outdoors due to their continuous downsizing and high functionality. Environments in which projectors are used often differ as regards the surrounding brightness. Projectors are recently required to be able to project an image whose brightness is suitable for such environments in which the projectors are used. In order to realize such a projector, there is sometimes used a light source whose luminance changes in accordance with supplied electric power.
In a projector using a light source whose luminance changes in accordance with supplied electric power, the brightness of the light source is controlled in general by changing the electric power supplied to the light source within a predetermined range of the rated electric power determined for the light source, for example, from approximately 80% to 60% of the rated electric power in view of control of the brightness and electric power saving (see Patent Literature 1). In the following description, 80% of the rated electric power is described as dimming electric power, and electric power of 60% or less of the rated electric power as saving electric power.